Cities across north-eastern Canada and the US are continuing to suffer from intense smoke brought on by hundreds of wildfires burning across Canada.

On Saturday, Toronto, New York and Washington DC recorded some of the worst air quality levels in the world, prompting health warnings from local authorities urging people to limit time outdoors because of the risks posed by the smoke.

Many of the wildfires remain out of control, forcing evacuations and destroying homes and infrastructure. The blazes left one tribal community completely decimated in northern Ontario, ripping through the Namaygoosisagagun First Nation with little warning.

Canadian officials said on Saturday that fire activity in Ontario was beginning to ease, with air quality expected to improve in US cities later in the day.

The smoke has also fuelled political tensions across the border. US President Donald Trump has threatened to impose new tariffs on Canada to offset what he described as the “incalculable” cost of the smoke’s impact on his country.

Poor air quality in the New York region is also prompting concerns for Sunday’s World Cup Final in New Jersey.

Where are the wildfires and how did they start?

There are 955 wildfires actively burning across Canada – nearly 200 of those in Ontario – according to the latest numbers from the Canadian Interagency Forest Fire Centre.

More than a dozen wildfires are actively burning along the northern edge of the bordering US state of Minnesota, spanning more than 73,000 acres. Officials have called the situation in Minnesota “unprecedented” and an emergency declaration is in place to help mobilise suppression efforts.

In Ontario, the fires are north of Lake Superior in more remote parts of the province, but within or close to national parks and First Nation communities. Officials said on Saturday that the fire activity in the province was beginning to slow.

So far, six communities are under evacuation orders with reports of damage to properties.

Matthew Hoppe, incident commander for the Namaygoosisagagun First Nation, told the BBC that his community was devastated by the wildfires in northern Ontario.

Community members had to “self-evacuate” via small boats on Monday afternoon with the fire rapidly approaching, Hoppe said, adding that there were no deaths or direct injuries, he says, but the community has been ”completely levelled”.

Wildfires are very common in Canada, but the number of outbreaks has rapidly increased in recent weeks.

A sea of red indicating wildfires from earlier this week

The National Interagency Fire Centre in the US and Natural Resources Canada predicted this was likely because of sustained hot weather at the end of June across northern Ontario, and below average rainfall.

This hot weather is being caused by a heat dome – an area of high pressure that gets stuck trapping warm air and the smoke underneath.

Extreme and long-lasting heat draws more moisture out of soils and plants – this dry vegetation acts as fuel for fires.

But this hot air can also become unstable causing the risk of storms which can produce strong winds – causing the fires and smoke to spread.

Where is the smoke and what is the impact?

High pressure further west across the Canadian prairies and the Northern Plains has kept the weather dry and hot, and allowed the wildfires to burn.

Satellite images over the past few days show the wind carrying smoke primarily south-east from Ontario across to Toronto, New York State and reaching Boston.

IQAir, a company which tracks global air quality, ranked Toronto, New York and Washington DC as the cities with the worst air quality in the world on Saturday due to the ongoing smokey haze hanging over.

Air quality in Minneapolis, Detroit, and parts of northern Minnesota was among the worst in the world earlier this week, but has improved significantly as of Saturday.

Wildfire smoke is hazardous for humans as it contains a mixture of very small polluting particles like PM2.5 and nitrogen dioxide.

“These particles when they get into our system get all the way down into our lungs, all the way down to our tiny breathing tubes and… they cause inflammation,” said Jim McDonald, New York State Department of Health commissioner, in a public address video on social media.

The smoke can exacerbate existing respiratory, heart, kidney and eye conditions, according to the World Health Organization.

Emergency responders, and vulnerable groups such as those with chronic illnesses and children – who are closer to the ground where the smoke can sink – are most at risk.

Governments will issue warnings depending on the air quality level which advises people on precautions to take. For example, an orange alert means people are advised to:

KN95 or N95 masks should be able to filter out 95% of these tiny particles – although there are still risks.

There are fraudulent copies being sold online so make sure it is government certified.

Many cities have activated their air quality emergency protocols and are distributing masks at local centres.

For further information on your local air quality alerts, consult this site if you’re in Canada, and here if you’re in the US.

The fires are also reigniting existing tensions between the North American neighbours.

US President Donald Trump on Friday threatened to impose new tariffs on Canada over what he called the country’s “willful negligence” in stopping the wildfire threat.

“The United States is being unnecessarily invaded by filthy, polluted, and unhealthy air,” Trump said, adding he would call Prime Minister Mark Carney over the country not engaging “in basic Forest Management”.

The threat followed complaints by US lawmakers over the wildfires. This week, four Republican lawmakers from Michigan state, which borders Ontario, wrote an open letter to Carney criticising Canada and “demanding immediate action” contain the fires’ impacts.

“American lungs are paying the price for Canadian inaction, year after year,” they wrote. Carney did not respond directly to the claims, but said that both countries had a responsibility to fight climate change.

Canada’s forests are largely controlled by the provinces; not the central government.

Ontario’s premier Doug Ford issued a response to the complaints and pushed back on claims Canada wasn’t doing enough to fight the threat, noting the massive response to the blazes and the region spending more than $1bn in recent years to mitigate wildfires.

On Saturday, Ford said it was “unacceptable” and “a shame” that US politicians were blaming Canada, particularly when Toronto helped them battle wildfires in California just last year.

“That’s what neighbours do,” Ford said. “You don’t get on and start threatening and criticising.”

Experts have told the BBC that blaming Canada for wildfire smoke misses the bigger picture.

“Weather doesn’t care about international borders,” says Patrick James from the University of Toronto. Once smoke reaches the atmosphere, it travels wherever the winds take it – and smoke from major US wildfires has also affected Canada in recent years.

Experts also say many of the current fires are burning in Canada’s vast, remote forests, where fires can be difficult to detect or contain before they become too large.

While better forest management can reduce wildfire risk in some areas, particularly near communities, it cannot prevent fires across an ecosystem of this scale.

How long is it expected to last?

Air quality across Toronto, New York and Washington DC is predicted to begin improving on Saturday, with levels falling from the “unhealthy” range down into the “moderate” range by the afternoon and evening.

“We expect rain to bring some much-needed relief to New Yorkers experiencing poor air quality over the weekend, but with it we may see the possibility of severe storms, flooding and tornados,” New York Governor Kathy Hochul said on Friday.

Forecasters say the low pressure system will curl further northeastwards into Saturday and Sunday, and the worst of the air with the greatest number of smoke particles will clear from the Great Lakes area into south-eastern Canada.

Conditions should improve across new England too by the end of Saturday.

There was some concern that smoke might still linger on Sunday when the final for the football World Cup is scheduled at MetLife Stadium in New Jersey – especially because it is an open-air venue.

But rain coupled with a change in wind direction is likely to help conditions in the area.

The long-term fire outlook for the season suggests the wildfire risk will continue to be above normal in the Canadian Northwest Territories, Ontario and Quebec throughout July and August.

Are Canadian wildfires getting worse?

Wildfires are a natural part of boreal forests – of which Canada has vast swathes. However, they have worsened in recent years.

The 2023 fires razed 15 million hectares (37 million acres) – an area larger than England – while the 2025 blazes burned 8.3 million hectares (20.5 million acres).

In Canada, half of wildfires are sparked by lightning and the rest from human activity – but drier soils and vegetation increase the likelihood.

Increasing global temperatures as a result of climate change is making heatwaves more frequent and severe, contributing to such conditions.

Climate change is also increasing the temperature over winter.

These milder conditions in the first part of the year can stimulate earlier plant growth providing more fuel for burning, and reduces the amount of snow cover.

Snow, with its very white surface, helps to reflect the sun’s radiation and has a cooling effect. The less snow, the hotter it becomes.

Will the smoky haze affect the World Cup final?

The World Cup final is set to take place in the New York – New Jersey area, a region that has been affected by the smoky haze. Officials have been handing out free protective masks and warned residents to limit outdoor activities.

On Saturday morning, New York City had the second most-polluted air in the world, according to global air monitoring index IQ Air. The conditions were discussed at a meeting between White House officials and Fifa ahead of Sunday’s final match.

But conditions are improving and rain is forecasted that could potentially help clear up the skies before Spain and Argentina take to the pitch. (BBC)